Dredging and scouring

ABSTRACT

The present invention relates to dredging and scouring. In particular, we will describe dredging and scouring apparatus for removing sand, silt, clay and like materials from sea or river beds. There is described an apparatus comprising a body having a bottom face and comprising an outlet flow path in which is mounted thrust means to direct, in use, a wash of water downwards towards an area of sea or river bed or the like, orientation means to connect said apparatus, in use, to a support means to orientate said apparatus with respect to the sea or river bed, and at least one inlet flow path through which water is supplied, in use, to the thrust means; characterised in that the inlet and outlet flow paths are provided with respective openings in the bottom face of the body. In the preferred embodiments, the inlet and outlet flow paths are parallel, but of opposite directions,

BACKGROUND TO THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to dredging and scouring. Inparticular, we will describe dredging and scouring apparatus forremoving sand, silt, clay and like materials from sea or river beds.

[0003] A suction dredger is the most widely used apparatus for removingsuch material, suction being created by a motor and pump unit, somewhatlike a vacuum cleaner. A modified form of the suction method, which isused in tidal waters, is to provide a vertical length of pipe above thearea to be cleared near the lower end of which air is fed under pressureto pass upwardly through said pipe. This creates buoyancy within thewater column, which will act to lift the sand, silt and like materialand set it in suspension with the water, whereafter it may be carried upa pipe into a hopper. This method is reliable in reducing thepossibility of small/lightweight articles being lost, but is timeconsuming due to the relatively small diameter of the pipe, normallyaround 0.5 metres, and hence restricted area covered.

[0004] 2. Description of the Related Art

[0005] WO89/07691 discloses a method of and apparatus for dredging inflowing water comprising lowering a casing of a wing shape downwardlytowards the area to be cleared, the casing carrying thrust meansarranged so that the thrust means is directed downwardly, theorientation of the wing casing being adjusted in the water so that itpresents a surface relative to the flow which causes a resultantdownward vertical component of force to counteract the upward forceprovided by the thrust means, the thrust means directing a wash of watertowards the areas to be cleared so that the turbulence created clearsthe sand, silt or like material covering the area. Such apparatus iscommonly referred to as a ‘wing dredger.’

[0006] WO97/32091 describes a modification of this arrangement in whichadditional apparatus is provided to enable full adjustment of the wingdredger in a side to side manner.

[0007] Another method, which can be used in relatively shallow tidalwaters, e.g. up to about 10 metres in depth, comprises mooring a tug,ship or other vessel in a fixed position above the area to be clearedand deflecting the propeller wash downwardly using a suitable guideplate. The wash disturbs the material around the wreck, which materialis thereby lifted, set in suspension and carried away from the area bythe tide. A significant restriction of this method lies in the minimumdepth to which the vessel may operate.

[0008] Accordingly, the present invention seeks to provide an apparatussuitable for dredging or scouring sea or river beds in shallow waters.

BRIEF SUMMARY OF THE INVENTION

[0009] In its broadest sense, the present invention provides anapparatus comprising a body having a bottom face and comprising anoutlet flow path in which is mounted thrust means to direct, in use, awash of water downwards towards an area of sea or river bed or the like,orientation means to connect said apparatus, in use, to a support meansto orientate said apparatus with respect to the sea or river bed, and atleast one inlet flow path through which water is supplied, in use, tothe thrust means; characterised in that the inlet and outlet flow pathsare provided with respective openings in the bottom face of the body.

[0010] Preferably, the inlet and outlet flow paths are parallel, but ofopposite directions.

[0011] Preferably, the outlet flow path comprises a duct formed with anoutlet in the undersurface of a central section of the body.

[0012] Preferably, the thrust means comprises at least one impellerassembly comprising an impeller mounted within the duct or within ahousing in fluid communication with the duct.

[0013] Suitably, an adjustable flow director is provided adjacent theoutlet of the outlet flow path, the director being adapted to adjust thedirection of flow of the water wash from the outlet. Typically, the flowdirector comprises a louvre assembly. Typically, but not essentially,the director is mounted internally of the outlet from the undersurfaceof the body.

[0014] In one particular embodiment, the body is in the form of a winghaving an angled face at at least one of leading and trailing edgesthereof. Such face or faces may be provided by means of an additionalwing profile attachment to the body.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0015] The above and other aspects of the present invention will now bedescribed in further detail, by way of example only, with reference tothe accompanying drawings, in which:

[0016]FIG. 1 is a perspective view of an embodiment of an apparatus inaccordance with the present invention;

[0017]FIG. 2 is a front view of the embodiment of FIG. 1;

[0018]FIG. 3 is a side view of the embodiment of FIG. 1;

[0019]FIG. 4 is a plan view of the embodiment of FIG. 1;

[0020]FIG. 5 is a cross-section along line V-V in FIG. 3;

[0021]FIG. 6 is a cross-section along line VI-VI in FIG. 5;

[0022]FIG. 7 is an underneath view of the embodiment of FIG. 1;

[0023]FIG. 8 is a part detailed view of FIG. 5 illustrating in greaterdetail the principle features of the thruster assembly of the apparatusof FIGS. 1 to 7;

[0024]FIGS. 9 and 10 are perspective views illustrating combinations ofa plurality of the embodiment of FIG. 1 into multiple linear apparatus;

[0025]FIG. 11 is a perspective view illustrating a modification of theembodiment of FIG. 1 including additional wing extension elements;

[0026]FIG. 12 is a perspective view illustrating a combination of twoembodiments of

[0027]FIG. 1 into a bi-directional apparatus; and

[0028]FIG. 13 is a perspective view from underneath illustrating the useof an additional manual scraper on an apparatus in accordance with thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

[0029] Referring initially to FIGS. 1 to 7, an embodiment of theapparatus of the present invention is illustrated comprising a body ortank 10 of generally lightweight construction, steel being a suitableconstruction material. Tank 10 has side walls 11, front and rear walls12, top face 13 and bottom face 14 together defining a cavity 15.Sealable inspection or access covers 16 are provided on the top face 13.A duct 20 is formed extending upwardly from an opening or outlet 21formed substantially centrally in the bottom face 14 of the tank 10.Duct 20 terminates at its upper end within the cavity 15 with abell-mouth opening 22. A bell-mouth shape is preferably for reasons offluid flow, but not essential.

[0030] Two apertures 23 are formed in the bottom face 14 of the tank 10defining inlets to the tank. Adjacent the inlets 23 are providedinclined fillets 25. These act to prevent build up of material takeninto the tank, the inclined surfaces acting to direct material fallingthereupon towards the inlet. Typically, the fillets 25 are formed fromconcrete to provide additional ballasting. In the arrangementillustrated in FIGS. 5 and 6, fillets 25 form a complete ring aroundeach inlet. In the modification illustrated in FIG. 7, fillets 25 areprovided along only the leading and trailing edges of the apparatus,that is to say, along the junctions of the bottom 14 of the tank withthe front and rear walls 12.

[0031] Mounted within the duct 20 adjacent outlet 21 is an impeller 30driven by means of sheathed shaft 31 coupled through a flexible coupling32 to a prime mover device 33 such as an electric, hydraulic orpneumatic motor. A Denison M30 hydraulic motor has been found to beparticularly useful, but many alternatives are available and will beapparent to the skilled person. Advantageously, -the flexible coupling32 is adapted to shear above a predetermined level of applied torque toavoid damage should the shaft 31 become seized, for example by ingressof foreign objects. Typically, the motor is mounted on the upper surfaceof the tank 10 rather than inside the tank. As the apparatus will beworking in shallow depths of water, it is important that the motor willbe capable of operating both in air and underwater. Sheathed shaft 31 isretained centrally within the duct 20 by means of supporting fins orvanes 34. As shown, typically two sets of fins are used, an upper set 34a and a lower set 34 b.

[0032] An internal grille 24 is provided over each inlet 23 to preventingress of large particulate material. Typically, the grille is formedfrom a plurality of plates aligned with the long axis of the tank andinclined at around 45°. The plates may be in the form of adjustablelouvres such that their angle may be varied so as to adjust the degreeof reactive force and the rate of water entry into the tank. Preferablythe inclination of the plates on the two inlets shown in the describedembodiment are opposite. The slope on the plates acts to deflect theinflowing water and provide a reactive force to counter the turningmoment created by the impeller 30. As this reactive force varies withthe velocity of flow through the inlets, which in turn is dependent uponthe flow through the duct 20 and the rotational speed of the impeller,the system remains rotationally balanced regardless of the speed of theimpeller. Non-rotation of the tank 10 is particularly important when asingle module is being operated in deeper water from a single supportwire. Accordingly, it will be appreciated that provided an even numberof inlets 23 is the most suitable arrangement, typically two inletsdisposed either side of the outlet duct 20. To avoid destruction of thebalancing water flows, the tank may be divided into two separatecompartments by means of a central bulkhead wall 27 (FIG. 6) whichextends upwardly to substantially the same height as the bell-mouthopening 22 of the duct 20. The compartments remain in fluidcommunication above the bellmouth opening. Alternatively, the bulkheadwall 27 may extend to the top face 13 of the tank, in which case one ormore openings are provided in the bulkhead wall 27 above the bell-mouthduct opening to provide the necessary fluid communication. Furtheralternative inlet arrangements will, however, be apparent to thoseskilled in the art. In particular, of course, the grille 24 could beexternally mounted.

[0033] Grab handles 18 are provided on the forward and leading edges ofthe top face 13 of the tank 10. In the preferred embodiment, these areformed from hollow tubing in fluid communication with the inside of thetank 10. Non-return valves (not shown) are mounted upon the grab handles18 towards the outer ends thereof and allow air to vent freely from thetank during initial submergence, but close when the apparatus is inoperation due to the lower pressure inside the tank 10. This also allowsthe tank to be partially lifted out of the water during operation invery shallow waters without allowing the introduction of air into thetank 10 which would interfere with the water flows therewithin.

[0034] As is illustrated in FIGS. 9 to 12, several of the tanksdescribed above may be coupled together to provide an enlarged scouringand dredging device. FIGS. 9 and 10 illustrate coupling two or threetanks side by side to provide a wider coverage apparatus. FIG. 11illustrates a modification of the embodiment of FIG. 6 in whichadditional front and rear profiled wing extension elements 40 are added.The wing extension elements serve to provide give the apparatus aprofile generally similar to the ‘wing’ arrangement illustrated in theprior art described above.

[0035] In the arrangement illustrated in FIG. 12, two devices aremounted with opposed front faces but inclined by means of a shortconnector element 41 coupling the devices at each end along their bottomedges and a long connector element 42 coupling the devices at theirupper edges, such that the outlets 21 are both directed to impinge upona common or focal point. The twin apparatus can then be supported, forexample by means of wires 43, above an area to be scoured, such as apipeline 44 upon a seabed. With such an arrangement, as the washes ofwater from both apparatus are directed to the same point, the scouringeffect is enhanced.

[0036] Whilst such modular arrangements are particularly advantageous,they are not essential to the working of the present invention. It willbe appreciated that where modular operation is not required, the tank 10need not be generally hexahedral in shape, but may be of substantiallyany shape, such as generally circular.

[0037] Suitably, an adjustable flow director is provided adjacent theoutlet, the director being adapted to adjust the direction of flow ofthe water wash from the outlet. Typically, the flow director comprises alouvre assembly 17 (FIG. 3) and may be mounted internally or externallyof the outlet 21 from the undersurface of the body. Clearly thisarrangement may be omitted where, for example, internal grille isadjustable.

[0038]FIG. 13 illustrates the addition of a mechanical scraper 50 toassist in the excavation of particularly hard soils, such as very denseand/or cemented sands and very stiff to hard clays. The scraper 50consists of a bar or tube 51 mountable to the under surface 14 of thetank at the leading edge thereof A plurality of tines 52 are mountedupon the bar 51. The bar 51 is free to rotate upon its mounting and thusthe tines 52 are free to pivot within the constraints dictated by thedesign of the tank 10 and its various mounting points. The weight of thetines is such that the tines 52 normally hang vertically downwards. Thetines 52 have hardened steep cutting points 53 adapted for ripping andscarifying the seabed surface. By weakening and disaggregating thesurface, the impeller jet is more readily able to excavate the surfacematerial. With a scraper attachment provide on the leading edge of theapparatus only, the forward pass would be with mechanical assistance,but the return pass would include water jetting only as the tines wouldpivot away from engagement with the seabed. The scraper could be includea locking arrangement to prevent pivoting of the tines out of suchengagement, but more preferably scraper attachments 50 are mounted uponboth the leading and trailing edges of the tank 10 such that bothforward and rearward passes would provide the cutting facility.

1. An apparatus comprising a body having a bottom face and comprising anoutlet flow path in which is mounted thrust means to direct, in use, awash of water downwards towards an area of sea or river bed or the like,orientation means to connect said apparatus, in use, to a support meansto orientate said apparatus with respect to the sea or river bed, and atleast one inlet flow path through which water is supplied, in use, tothe thrust means; characterised in that the inlet flow path and outletflow path are provided with respective openings in the bottom face ofthe body.
 2. An apparatus as claimed in claim 1 wherein the inlet andoutlet flow paths are parallel, but of opposite directions.
 3. Anapparatus as claimed in claim 1 wherein the outlet flow path comprises aduct formed with an outlet in the undersurface of a central section ofthe body.
 4. An apparatus as claimed in claim 2 wherein the outlet flowpath comprises a duct formed with an outlet in the undersurface of acentral section of the body.
 5. An apparatus as claimed in claim 1wherein the thrust means comprises at least one impeller assemblycomprising an impeller mounted within the duct or within a housing influid communication with the duct.
 6. An apparatus as claimed in claim 1wherein an adjustable flow director is provided adjacent the outlet ofthe outlet flow path, the director being adapted to adjust the directionof flow of the water wash from the outlet.
 7. An apparatus as claimed inclaim 6 wherein the flow director comprises a louvre assembly.
 8. Anapparatus as claimed in claim 6 wherein the director is mountedinternally of the outlet from the undersurface of the body.
 9. Anapparatus as claimed in claim 1 wherein the body is in the form of awing having an angled face at at least one of the leading and trailingedges thereof.